Perforating guns have an array of explosive charges thereon. The explosive charges can fire projectiles or form a jet of liner material (such as copper). The guns are lowered inside of a cased well to a depth containing a pay zone of oil or gas. The explosive charges are detonated wherein the casing is perforated at the pay zone. Upon the completion of the well, oil and gas can then flow through the perforations into the casing and up to the surface.
Great care is taken with the explosive charges in the perforating guns in order to prevent their accidental detonation. An accidental detonation with the gun on the surface could result in the injury of a crew member. An accidental detonation in the well in an undesirable location could result in a loss of production of the well. Therefore, initiators are used to better control the detonation of the perforating guns. One type of initiator is known as a detonator, which is an electrical device.
Detonators are initiated by an electrical current. An electrical current heats a resistive element inside the detonator to a temperature that is sufficiently high to ignite a charge inside of the detonator. The detonator is located physically close to an end of a detonating cord so as to ignite the detonating cord. When ignited, the detonating cord propagates the detonation from the detonator to fire the explosive charges that are distributed along the length of the perforating gun.
One type of detonator has a spring loaded pin or button on one end and an explosive charge on the other end. For safety reasons, the detonator is internally grounded until the button is depressed. Thus, when internally grounded, the detonator is in a safe mode and is unable to detonate. This type of detonator is conventional and commercially available as part number DET-3050-008 from Owen Oil Tools of Fort Worth, Tex.
The detonator is located in a detonating block, which is located in a firing head at an end of the perforating gun. The detonator is contained within the detonating block and is adjacent to an end of the detonating cord in the perforating gun. A long rod, or arming and contact pin, is used to press the button on the detonator in order to arm it. Thus, the detonating block secures the detonator in place adjacent to the detonating cord and positions the detonator relative to the arming and contact rod.
Conventional detonating blocks function as collars to hold the detonator in place. Consequently, conventional detonating blocks have a passage extending from one end of the block to the other. Upon detonation, some of the hot gases from the detonator and the detonating cord blow back in the direction of the arming and contact pin, damaging the pin and its associated spring in the process.
When the perforating gun is brought back out of the hole to the surface after a detonation, such damage must be fixed before the gun can be reused. Often times, a well requires multiple perforations, requiring the perforating gun to make more than one trip downhole. Minimizing the damage to the detonating mechanism minimizes turnaround time for the perforating gun on the surface and equipment loss.